Leptohadronic Blazar Models Applied to the 2014–2015 Flare of TXS 0506+056

Xavier Rodrigues,Walter Winter,Anatoli Fedynitch,Shan Gao,Andrea Palladino

doi:10.3847/2041-8213/ab1267

Xavier Rodrigues, Walter Winter + Show 3 more

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https://doi.org/10.3847/2041-8213/ab1267

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Abstract

We investigate whether the emission of neutrinos observed in 2014–2015 from the direction of the blazar TXS 0506+056 can be accommodated with leptohadronic multiwavelength models of the source commonly adopted for the 2017 flare. While multiwavelength data during the neutrino flare are sparse, the large number of neutrino events (13 ± 5) challenges the missing activity in gamma-rays. We illustrate that two to five neutrino events during the flare can be explained with leptohadronic models of different categories: a one-zone model, a compact-core model, and an external radiation field model. If, however, significantly more events were to be accommodated, the predicted multiwavelength emission levels would be in conflict with observational X-ray constraints, or with the high-energy gamma-ray fluxes observed by the Fermi Large Area Telescope, depending on the model. For example, while the external radiation field model can predict up to five neutrino events without violating X-ray constraints, the absorption of high-energy gamma-rays is in minor tension with the data. We therefore do not find any model that can simultaneously explain the high event number quoted by IceCube and the (sparse) electromagnetic data during the neutrino flare.

Highlights

The object TXS 0506+056 is an active galactic nucleus (AGN) of the blazar type, classified as a BL Lac object, with a measured redshift of z = 0.3365 (Paiano et al 2018)
We implement an energy-independent escape rate for charged particles of te¢sc = fesc tF¢S, with fesc > 1.3 Figure 1 clearly demonstrates that the models compatible with the spectral energy distribution (SED) produce too few neutrinos, where at most 1.8 events are expected during the duration of the neutrino flare. This number is limited by the X-ray constraint on the SED, which we derive from the nondetection by Swift Burst Alert Telescope (BAT)
This example demonstrates the importance of electromagnetic data across the entire spectrum to constrain theoretical models, as the electromagnetic cascade accompanying the neutrino production can be hidden in unconstrained energy ranges

Summary

Introduction

In 2017 September, a muon neutrino with a reconstructed energy of about 290 TeV was observed by IceCube from a position compatible with this source in coincidence with a period of flaring in multiple wavelengths (Aartsen et al 2018a) at a significance level of 3σ. This event has enticed the multimessenger community to explore the potential of TXS 0506 +056 as a source of astrophysical neutrinos. The current theoretical consensus is that the geometry of the radiation zone must be more complex, involving a compact radiation core with high photohadronic interaction rates (Gao et al 2019), or external radiation fields boosted into the jet frame, either thermal (Keivani et al 2018) or nonthermal (Ansoldi et al 2018)

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